In many industrialized countries throughout the world the number of meals prepared and consumed outside of the home has steadily increased and is now estimated to exceed the number of meals prepared in the home. Many restaurants have been established to prepare, serve and/or deliver hot food to consumers. Particularly, significant for modern food consumption of prepared food are establishments known as fast food restaurants. Popular hot foods such as fried chicken, hamburgers, pizzas, and tacos are among some of the "staples" of the fast food industry. Purposes of cooking food and serving it hot are the same for home cooking, restaurants and fast food restaurants and include killing potentially harmful bacteria and certain viruses, terminating the growth of such potentially harmful microbes, and enhancing the flavor or otherwise improving the palatability of food.
Many devices have been designed to keep prepared food warm including metal containers heated with gas flames, electrical resistance coils, steam or other heat sources that rely primarily upon heat conduction through the metal container to keep the food warm. Those devices invariably result in hot exposed surfaces and generally require that the food be dished out of the container prior to serving. Such heat conduction warming devices are not well suited for transporting the food. Also, in the fast food industry, it is generally preferred to provide the food in individual entre containers or in individual serving size containers that are light weight and disposable. Typically such disposable food containers can be made of paper, cardboard or other materials that are not well suited for conductive warming.
It has been found that many of the types of "fast foods" that are desirably prepared in advance, cooked at high temperatures exceeding 160.degree. F. and kept warm at above about 120.degree. F. until the food is ordered at a restaurant, handed to a carry out customer or otherwise delivered, are also well suited for warming using infrared radiation. Currently warming is accomplished with infrared lamps, typically aimed from above at the precooked food on a shelf or in a holding area. For example, pizzas, tacos, hamburgers, or fried chicken may be place on a stainless steel counter-top or shelf with one or more infrared lamps aimed at the area to keep the cooked products warm until it is carried to a restaurant customer for consumption, picked up or delivered. The prepared hot food might also be placed in a buffet type covered serving area with infrared lamps spaced above to keep the food warm while the serving line is available. Hot prepared food is often packaged hot in a cardboard container, in paper wrapping or in a paper bag to be handed to the customer or to be carried by a delivery driver to a telephone ordering customer for consumption off the premisses.
Infrared heat lamps as, with conductive heating, can serve to keep food warm but there are certain drawbacks and shortcomings that result in practical situations. For example, the counter-top or shelf or other surface that serves to hold the food also become heated and can become hot enough to cause burns when touched by people. Also the lamps are typically constructed of colored glass bulbs shielded on the sides but exposed downward or upward to allow the food to receive the infrared radiation. The exposed surface in a food serving area requires cleaning. It has been found that this is a task often delegated to new or inexperienced workers who can unknowingly apply a damp cleaning cloth to the hot glass surface or directly apply a wet cleaning solution thereto while the lamp is on or after it is turned off but before it has completely cooled. The localized cooling and contraction of the lamp surface can cause the bulb to shatter thus creating a dangerous situation sometimes resulting in injury and invariably resulting in a significant amount of lost time, effort and expense to clean the broken glass, to replace the lamp and to replace any food that might have been contaminated with bits of broken glass.
Moreover an infrared lamp warming apparatus requires a durable structure having a significant size that is not well adapted for transportation as in a mobile delivery vehicle.
Other know infrared heating devices with metal electric resistance elements also suffer from size and structural limitations as well as risk of burning from contact with the elements or from absorption of heat by metallic food holding shelves.